Temperature responsive device



NOV. 2, 1943. BRAN'NQN r 2,333,291

TEMPERATURE RESPONS IVE DEVICE Filed June 19, 1940 2 Sheets-Sheet l m mum \E INVENTOR HERBERT E. BRANNON PWUKW/W ATTORNEY Nov. 2, 1943. H. E. BRANNON 2,333,291

TEMPERATURE RESPONSIVE DEV ICE Filed June 19, 1940 2 Sheets-Sheet 2 INVENTOR I07 5E HERBERT E. BRANNON ATTORN EY Patented Nov. 2, 1943 D STATE UNlTji s PATENT OFFICE TEMPERATURE RESPONSIVE navrca Herbert a. Brannon, Detroit, Mich.

Application June 19, 1940, Serial No. 341,213

' Claims, (01. zoo-13s) This invention relates to temperature responsive devices of the type having as an essential part a laminated metal element adapted to deflect under the influence of variations in the provide a temperature control for the heatingelements of electric heating circuits which not only acts under the influence of variations in the temperature of the heating element or device heated thereby, but under the influence of variations in the 'power input to the heating element of the circuit as well. Another object is the provision of a temperature control for an electric heating element which is directly responsive *to variations in the power input to the heating circuit and acts substantially instantaneously upon a. change in the power input.

Basically the invention resides in a laminated metal element having a contact at its center and (plurality of arm radiating therefrom. The laminated element is mounted on a supporting structure solely by means of the extremities of the arms. The element is mounted in a manner to permit a slight radial shifting of the ends of the arms relative to the support so as to permit flexing of the element.

The foregoing objects will more fully appear in the -following specification, reference being made to the accompanying drawings, wherein:

Figure 1 is a cross-sectional view of an adjustable thermostat embodying the invention;

Figure 2 is an exploded view of the thermostat shown in Figure 1, certain parts being omitted;

Figure 3 is a plan view of the laminated temperature responsive element employed in the device shown in Figures 1 and 2;

Figure 4 is a cross-sectional view of a somewhat modified form of the invention taken on the line 4-4 of Figure 5;

Figure 5 is a plan view of the device shown inFigure 4;

Figure 6v is a cross-sectional view of a still further modified form of the invention;

Figure 7 is an exploded view of the device shown in Figure 6, certain parts being omitted;

Figure 8 .is a plan view of the laminated temperature responsive element embodied in the device shown in Figures 6 and '7;

Figure 9 is a front elevational view of a cooking vessel to which a modified form of the invention is applied, parts of the vessel being broken away to show the interior construction;

Figure 10 is a cross-sectional view of the modifled control employed with the device of Figure 9;

Figure 11 is an exploded view of the control shown in Figure 10;

Figure 12 is a cross-sectional view of the wire used in the heating element of the device shown in Figure 9; and

Figure 13 is a wiring diagram of the device shown in Figure 9.

Referring now more in detail to the drawings, and particularly to Figures 1 to 3 thereof, the invention comprises a temperature responsive element Ill. The element I0 i a laminated metal piece made up of two sheets of metal having dissimilar coefllcients of eripansion andsuitably bonded together. The element In is shaped to provide a central portion ll having a plurality of arms I2 radiating therefrom, the extremities of e the arms being space apart, preferably equidistantly, A holed} 1 \formed in the center of the element 10 to receive a contact ii. The hole I3 is substantially larger than the shank of the contact l4, and in order to insulate the contact from the element ill a pair of washers iii of mica or similar insulation are located between'the heads of the contact l4 and the element iii. A connecting strip I6 is secured to the contact and extends outwardly therefrom.

The element I0 is mounted within a housing IT. The latter consists of three parts, a main body portion I8, a retaining ring i9 and an internally threaded bushing 20. The main body portion i8 is provided with a peripheral flange 2| at its open end, and an oiiset shoulder 22 intermediate its ends. The retaining ring it consists of a cylindrical portion 23 fitting within the body portion l8, and a peripheral flange 24 in juxtaposed parallel relation to the flange 2|. The bushing 20 is secured in any suitable manner to the end of the housing opposite the retaining ring l9.

The, temperature responsive element I0 is mounted within the housing H, with the extremities of the arms I! located between the offportion 20 of the retaining ring I0. Theelement insulated from the latter by washers 20 of mica.

or similar insulating material. The connecting strip I6 is attached to the terminal screw 26.

Secured to the screw 25 is a flexible strip 29 of spring metal carrying a contact 30 at its free end. The contact 30 is arranged in a position permitting it to touch contact I4 under certain conditions. The spring metal strip 20 is stressed so that it tends to'spring away from the contact I4.

Threaded into the bushing 20 is an adjusting screw 3i arranged in alignment with the contacts I4 and 30. In its inner end is a socket which receives an insulating bar 02. The latter normally bears against the flexible strip 20. The outer end of the adjusting screw SI is knurled in order that it may be easily rotated.

The device just described is adapted for use in any electrical temperature control circuit. The flanges 2| and 24 of the housing are secured to any suitable support by screws, bolts, or other fastening means, not shown. The terminal screws are connected to wires in the control circuit, so that current flowing therein must pass throu h the strips I and 20 and the contacts I4 and 30. If the contacts do not touch each other no current can flow in the circuit.

The laminated metal temperature responsive element I0 is adapted to deflect in a direction away from the contact 00 as the temperature of element I0 rises due to ambient temperature, and deflect in the opposite direction as its temperature decreases. Thus, upon predetermined increase in the temperature oi. the laminated element the contacts will separate and break the circuit controlling the temperature of the space surrounding the thermostat. The temperature at which the circuit will be broken can be regulated by turning the screw 0| in or out as desired.

If turned in toward the contacts I4 and 00. a

greater deflection and correspondingly higher temperature of the laminated element I0 is required to break the' circuit. This is due to the fact that the element I0 is placed under an initial stress or deflection which must be overcome before there will be any movement of the contact I4.

Figures 4 and 5 show a slightly modified form of the invention. As a whole the construction illustrated in Figures 4 and 5 is substantially identical to that previously described. In this device, however, a screw 0| having threads of less pitch than screw 00 is employed. Therefore, the same amount of rotation, the range or temperature controlled by the screw II is less than that of 1118 previous device. As a result. the adjustment of the screw can be more closely regulated than in the previous device.

This modification of the invention is also provided with a pair of limit screws 35, for adjusting the off position of the thermostat. The screws 35 are threaded through the housing on opposite sides of the screw-0| and their inner v ends are located in a position to engage opposite arms of the laminated element I0. By means of the screws 35 the element I0 may be placed under predetermined initial stress requiring the attainment of a desired temperature before deset shoulder 22 and the free end 0! the cylindrical flection of the element I0 can begin. Thus. the screw 0| may be used to regulate the temperatures above that for which the screws 00 are set. but when the screw II is backed out sumciently to permit contact 00' to disengage contact I4. the circuit is broken. For instance. if the screws 00 are set so that a temperature of 70 is required to deflect the element I0, the screw ll may be used to increase this stress, or in other words,

regulate the temperatures above 70". However, as soon as screw ii is backed out to a setting which normally would hold the temperature at 69 the circuit is broken. This allows the circuit to be broken if desired without turning back the screw 3| several turns, or if the thermostat is designed to operate only within a 360 adjustment of the screw 3|, it permits elimination of the master switch which otherwise would be necessary.

The device illustrated in Figures 6, 'l and 8 is a slightly modified form of the invention. It difiers from. those previously disclosed in the shape of the laminated metal element and in the type of adjusting screw.

The device comprises a laminated metal element 50, having a central portion 5| and four arms 52. The element carries a contact 03 at its center and a connecting strip 04 similar to those previously described. The element 50 is mounted in a housing to which are secured two terminal screws 58 and 51. A resilient strip 58 connects one terminal 51 to a contact 00 engageable with contact 53.

A bushing 60 is welded to the housing 55. The bushing is screw threaded to receive a screw GI. The inner end of the screw SI has a recess to receive an insulating rod 02. A slot 63 is provided in the outer end of the screw to accommodate a screw driver.

In general the operation 01 the species shown in Figures 6 to 8 is the same as those previously shown. However, the range of adjustment is not so great as the previous modifications. This device is intended primarily for use as a flxed thermostat, which once set is not to be changed. The adjusting screw is therefore of less length than the screw used in the previously described device and has no knurled knob.

Figures 9 to 13 illustrate a further modified form oi. the invention. It is shown in connection with an electrically heated cooker I00. The cooker comprises an outer shell having a side wall I02 and a bottom wall I03. Supported on the upper edge of the side wall I02 is an inner pan and heating element support I04. The inner pan is held in place within the outer shell by a screw I05 extending through the bottom wall I03 and threaded into a bracket I00 secured to the bottom of the inner pan I04.

The heating element consists of coils of resistance wire I0I wound about the sides and bottom of the inner pan I04. The resistance wire is covered with suitable thermal and electrical insulating material I08 (see Figure 12), such as asbestos, and is wound directly on the inner pan I04.

A removable cooking pot I09 is placed within the inner pan I04, and a removable cover H0 is placed over the entire assembly.

Mounted on the side wall of the inner pan I04'is the temperature control device III. It comprises a housing made up of three parts, a main body II2, an annular retaining ring H0, and an internally threaded bushing H4. The main body portion II2 has a shoulder II5 interends. A pair of openings III are the retaining ring. The retaining ring III ilts over a ilangeIII at theopen end of the main body I I2 and is secured thereto.

Mounted in the groove formed by the shoulder III and the retaining ring II! are an insulating ring IIO, a metal connecting ring H0, is. laminated metal temperature responsiveelement I20 which is a resistor, another metal connecting ring I2I, and a second insulating ring I22. in the order named.

The laminated metal element I20 is formed from three sheets or metal I20, I24 and I25. Two or the sheets I20 and I24 have the same coeilicient of expansion, but a different cient than sheet I20. One or th two sheets I22, I24 has a higher internal resistance than "the other. The element I20 is formed as in Figure 3 or Figure 8,, having a plurality oi angularly separated arrns radiating from its center. At thesauteris acontact I20.

The connecting rings H and I 2I are of angular cross-section and are adapted, when placed element I20. The element I20 fits loosely between the rings H0 and I2I to permit a slight radial shifting thereof so that the element I20 may flex slightly. The ring H0 is provided with an integral connecting link I2I extending axially thereof.

The insulating ring III is of angular crosssection. The insulating ring I 22 is flat. When placed together as in Figure the two insulating rings II 0 and I22 surround the metal connecting rin s I I0 and HI and the laminated element I and separate them from direct contact with the parts H2 and N0 of the metal housing,

In th holes I I0 in opposite side walls of the main body portion I I2 of the housing are terminal screws I20 and I20. They are insulated from the housing by washers I00 of mica or other suitable insulation. The terminal screw I20 is connected to the connecting link I21. The terminal screw I20 is connected to and supports a spring metal strip IOI within the housing. At its free end the spring metal strip I3I carries a contact I02 which is adapted under normal con- I'he bushing H4 3 together, to enclose the ends of the arms on the I20 and III by way or resilient spring metal strip III, contact I02, contact I24, element I20, egrlinecting rings III-III, and connecting link The manner of addustment oi the thermostatic control III is the same as those previously described. That is, the contact I02 is moved toward or away from contact I 20 by rotation or screw I22. The screw Ill'is rotated by handle I20.

Also, under ordinary conditions the operation of the thermostatieicontrol III is 'the sam as the other controls.,. .'1he laminate metal element I20 is caused .to ii variations in'its temperature created by th eat transmitted to it from the cooking vessel Thus. the circuit including the heating element-is made or broken by the thermostatic c ntrolHIi'I' to maintain a substantiallygoonstantbmperature. g;

Under certain c ions, however, the control II I shown in Figures to 12 produces, an additional result not "obta fie by be previousl described. controls. resi'iltis the compensation to; variations input caused by changes in line voltage or" circuits in the heating element I0I.-

When the current is on and flowing through I the heating element I0Ifit also passes through the element I20 and heats it slightly" because of I its own internal 're ista se. The heat produced ditlons to touch the contact I20 on the laminated I32 away from the contact I20.

Threaded into the bushing H4 is an adiusting screw I03. The inner end or the screw I30 has a recess that receives a short rod of insulating material I04 which is adapted tobe pressed against the" back 01 the sp ing metal strip I3l. The outer end of the adju ting screw I03 is Drovided with a handle I35. The handle provides for rotation oi the screw I00 and has a pointer I80 thereon which cooperates with a dial (not shown) on the outer shell I02 to indicate the setting of the thermostat.

The temperature control III is connected in series with the heating element III! as indicated in Fi ure 13. The laminated element I20 is in the circuit by virtue of its connect on w th the terminal screw I20 through the connecting l nk I2I. Thus, the current for energizing the heat- ..ing element I0I must flow through the laminated in this manner under normal conditions is relatively slight and ha 'practically no effect on the bending of the element I07. However, if the power input from the line should increase sharply as it sometimes does, the additional current causes the element I20 to heat up appreciably and deflect away from the contact I22, thereby break-- in: the circuit.

The advantage of this arrangement lies in the fact that the control of the temperature within the cooking pot is maintained more constant than it would be by a thermostat under the iniluence of ambient temperature only. Where the power input from the line increases sharply, as it does when the load on the line drops, the heating element I0! becomes hotter and transmits more heat to the cooking pot I00. However, it requires a' certain amount of time for the additional heat to raise the temperature of the cooking pot I00 to the point where it alone will actuate the switch III. Ordinarily by the time the temperature of the cooking pot I00 could be raised suiiiciently to actuate the switch, a considerable quantity of heat would be stored in the heating element I07 and pan I04. The heat thus stored would cause the pot I00 to overheat even though the current was 011'.

Such a result is overcome by the presence of the laminated resistor element I20 in the circuit. Any increase in the power input in the circuit causes the resistor to heat up and flex so as to break the circuit even before the control switch would be actuated by ambient temperature alone. No excessheat is stored in the heating element and as a result the cooking pot I00 cannot overheat.

The same result occurs if a short circuit in the heating element develops. A short circuit permits more current to how through the laminated resistor element I2II, thereby increasing its temperature and causing it to flex and break the circuit.

The modification shown in Figures 9 to 12 has still another effect not obtained in the prewalls of the inner vicusly described devices. It eliminates the need for accurately measuring the resistance of the wire employed in the heating element with which the control is associated.

Resistance wire for electric heating elements is usually drawn or rolled and its cross section varies somewhat. This producesv variations in the resistance of unit lengths of the wire. Hence, in order to produce heating elements of equal heating capacity, it is necessary to measure the resistance of the wire in each individual unit and cut it to the requisite length. If this is not done, different coils will produce different temperatures under omerwise identical conditions.

When a thermostatic control such as illustrated in Figures 9 to 12 is employed with a heating element, it is unnecessary to provide equal resistances in all heating elements of like kinds, because the laminated resistor I compensates for ordinary variations in resistance.

Thus, if the resistance of the heating element,

is more or less than the desired amount, the current flowing in the circuit will varyinversely in relation to the amount of resistance. Therefore, the laminated resistor I20 will be heated to a greater or less degree, depending on the current flowing through it, and will make and break the circuit intermittently at a rate which will maintain the desired temperature in the heating element. resistor I20 is exposed to the heat from the, heating element or not. As a result, the wires used in diflerent heating coils of the same desired heating capacity can all be cut to a definite length.

The invention desired above, because of its unique construction, is more compact and less costly than previous devices employed in the same general way. Instead of a long narrow strip supported at one end only, the temperature responsive element consists of a central contact and a plurality of arms radiating therefrom and supported at the extremities of the arms. The amplitude. of movement of the latter construction, for a given temperature change, is greater than that of a strip of the same length and supported at one end only. Thus, a smaller housing may be employed, and less of the relatively expansive laminated metal may be used. Furthermore, the deflection under temperature changes is morepositive as well as more constant than previous types of temperature responsive elements.

The scope of the invention is indicated in the appended claims.

I claim:

l. A temperature responsive device comprising a laminated metal element'and a support therefor, two laminae of said element having different coefficients, of thermal expansion, said element including a plurality of'arms radiating from its center, said arms having circumferentially spaced apart outer extremities engaging said support and being movable independently of each other relative thereto in the plane of said element, said engagement of the armswith the support constituting the sole means for supporting said element.

2. A temperature responsive device comprising a laminated metal element and a support therefor, two laminae of said element having different ,coefilcients of thermal expansion, said element including an electrical contact at its center engageable with another electrical contact on said This will occur whether the support, and a plurality of arms radiating from said contact, the extremities of the arms being mounted on said support and movable independently of each other relative thereto in the plane oi. said element.

3. A temperature responsive device comprising a laminated metal element and a support therefor, two laminae of said element having different coeflicients of thermal expansion, said element including an electrical contact at its center en geabie with another electrical contact adjustably mounted on said support, and a plurality of arms radiating from the contact on said element, the extremities of said arms being mounted on said support and movable independently of each other relative thereto in the plane of said element. and means on said support for varying the position of the contact on the support relative to the contact on the laminated element. 1

4. A temperature responsive device comprising a laminated metal element and a support therefor, two laminae of said element having diilerent coeflicients of thermal expansion, said element including an electrical contact at its center and a plurality of arms radiating therefrom, the extremities of said arms being mounted upon said support and movable independently of each other relative thereto in the plane oivtheelement, and

another electrical contact mounted upon said support and adjustable toward and away from said first mentioned contact. 5. A thermostat comprising a laminated metal .element and a housing therefor, two laminae of said element having different coefficients of thermal expansion, said element including an" electrical contact at its center and a plurality of arms radiating therefrom, the extremities of said arms being mounted on said housing and forming the sole support for said element, a pair of spaced terminals secured to said housing, a connection between one terminal and said contact, a second contact adjacent said first mentioned contact, resilient means biasing said second contact away from said first contact and connecting said second contact to the other terminal, and adjustable means on said housing for moving said second contact toward the first contact against the action of the resilient means.

6. In a thermostat, a laminated metal element and a support therefor, two laminae of said ele-' *ment having diiferent coefficients of thermal expansion, said element comprising a plurality of arms radiating from its center, the extremities of said arms being mounted on said support and forming the sole support for said element, the

extremities of the arms being movable inde- I cluding an electrical contact at its center in engagernent with another electrical contact mounted on said support, and a plurality of arms radiating from the contact on said element, the extremities of 'said arms being mounted on said support and movable independently of each other relative thereto in the plane of said element, said element being adapted to deflect under the influence of variations in the temperature thereof whereby to move the contact thereon toward and away from the contact on the support, means on said support for varying the position of the contact on the support relative to the contact on the Aaminated laminae of said element element, and adjustable means on said support for limiting the movement of the contact on said element toward the contact on the support.

8. A thermostat comprising a support, a first contact on said support, a second contact, and means for moving said second contact into and out engagement with said first contact, said means consisting of a laminated metal element secured at its center to said second contact, two laminae of said element having diilerent coefiicients of thermal expansion, said element including a plurality of arms radiating from its center, said arms having circumierentially spaced apart outer ex-. tremities engaging said support and being movable independently of each other relative thereto in the plane of said element, said engagement of the arms with the support constituting the sole means for supp rting said element.

9. A thermostat comprising a support, a first contact on said sup a second contact, and means for moving said second contact into and out of engagement with said second contact, said means consisting of a laminated metal element secured at its center to said second contact, two

having different coefiicients 0! thermal expansion, said element having a plurality of arms radiating irom its center, said arms having circumrerentially spaced apart outer extremities engaging said support and being movable independently of each other relative thereto in the plane of said element, said engagement oi the arms with the support constituting the sole means for supporting said element, said first contact being adiustably mounted on said support for movement relative thereto in a direction toward and away from said second contact.

10. A thermostat comprising a support, a first contact on said support, a second contact, means for moving said second contact into and out 01 engagement with said first contact, said means consisting oi a laminated metal element secured at its center to said second contact, two laminae of said element having diflerent coemcients of thermal expansion, said element including a plurality of arms radiating from its center, said arms having circumierentially spaced apart outer extremities ensaging said support and being movable independently of each other relative thereto in the plane of said element, said engagement of the arms with the support constituting the sole means for supporting said element, and means adiustably mounted on said support for limiting the movement or the second contact toward the first contact.

HERBERT E. BRANNON. 

